The present invention relates to a semiconductor integrated circuit device and a contactless electronic device, and, more particularly, to a technique utilized effectively in a stable power supply circuit of a contactless IC card and semiconductor integrated circuit devices mounted on the contactless IC card.
In recent years, a so-called IC card on which semiconductor integrated circuit devices are mounted has come to be widely used. The IC card attains an exchange of information between a reader/writer and the semiconductor integrated circuit devices and realizes various functions equal to those presently performed by a magnetic card. In a contactless IC card having no external electrode through which a signal and a voltage are supplied to the IC card, an antenna mounted in the IC card receives an electromagnetic wave supplied from the reader/writer, and a voltage generated across the antenna is rectified to produce an internal voltage required for the operation of an inner circuit including semiconductor integrated circuit devices mounted on the IC card. In this case, when excessive electric power is supplied to the inner circuit from the reader/writer so that a power supply voltage higher than the breakdown voltage of the devices constituting the inner circuit is supplied to the inner circuit, the devices are broken. In order to prevent such a breakdown, it is necessary to monitor the power supply voltage level and to control it to prevent a power supply voltage higher than the breakdown voltage from being supplied to the inner circuit.
The inventors of the present invention have studied a power supply circuit, as shown in FIG. 17, on the basis of the technique disclosed in JP-A-11-353041, published on Dec. 24, 1999. In this circuit, an anode terminal of a diode D01 is connected to an input terminal IN1, and a cathode terminal of the diode D01 is connected to an output terminal OUT1. An anode terminal of a diode D02 is connected to a junction N04 and a cathode terminal thereof is connected to an input terminal IN2. A condenser C01 is connected between the output terminal OUT1 and the junction N04 to constitute a half-wave rectifier circuit.
The following circuit is provided in order to stabilize internal voltages. A source terminal of a P-channel MOSFET (hereinafter referred to as PMOS transistor) MOI is connected to an output terminal OUT2, and a drain terminal thereof is connected to the junction N04. Resistors R01 and R02 constituting a voltage divider are connected in series to each other between the output terminals OUT1 and OUT2. A divided voltage generated at a junction N01 of the resistors R01 and R02 is supplied to an inverting input (xe2x88x92) of the voltage comparator circuit (operational amplifier circuit) A01. A reference voltage VREF is supplied to a non-inverting 5 input (+) of the voltage comparator circuit A01, and a comparison output voltage of the comparator circuit is applied to a gate of the PMOS transistor
In the power supply circuit shown in FIG. 17, an input signal applied between the input terminals IN1 and 1N2 is rectified by the half-wave rectifier circuit and is smoothed by the condenser C01. The smoothed voltage is obtained as a voltage difference V12 between the output terminal OUT1 and the junction N04. The smoothed voltage V12 is given by
V12=VINxe2x88x92VF1xe2x88x92VF2xe2x80x83xe2x80x83(equation 1)
where VIN is an amplitude of an input voltage applied between the input terminals IN1 and IN2, VF1 is a forward voltage of the diode D01, and VF2 is a forward voltage of the diode D02.
Thus, when the input voltage VIN is increased, the voltage difference V12 is also increased. Accordingly, when power supply terminals of the inner circuit are connected to the output terminal OUT1 and the junction N04 so that the voltage difference V12 is directly supplied thereto as a power supply voltage, the voltage difference V12 sometimes exceeds the breakdown voltage of the devices constituting the inner circuit to thereby break the devices. In order to prevent a voltage exceeding the breakdown voltage from being applied to the devices constituting the inner circuit, a voltage control circuit is provided including the PMOS transistor MOI and the voltage comparator circuit A01.
In the voltage comparator circuit, when a voltage divided by the resistors R01 and R02, connected between the output terminals OUT1 and OUT2, is higher than the reference voltage VREF (the absolute value of the divided voltage is lower than the absolute value of the reference voltage), the output voltage of the voltage comparator circuit A01 is reduced, so that the voltage produced by the half-wave rectifier circuit, that is, the voltage across the condenser C01, is reduced by a voltage (threshold voltage) between the gate and the source of the PMOS transistor to be outputted. On the contrary, when the divided voltage is lower than the reference voltage VREF (the absolute value of the divided voltage is higher than the absolute value of the reference voltage), the output voltage of the voltage comparator circuit A01 is higher than the voltage at the input terminal IN2, so that the gate voltage of the PMOS transistor MOI is limited to a fixed voltage. Accordingly, the power supply voltage of the inner circuit supplied through the output terminals OUT1 and OUT2 is limited to a fixed voltage in order to make the divided voltage equal to the reference voltage VREF. Thus, the output voltage VOUT obtained from the output terminals OUT1 and OUT2 is stabilized to satisfy the equation (2).
VOUT=VREFX(R01+R02)/R01xe2x80x83xe2x80x83(equation 2)
In the above circuit operation, by adjusting a resistance ratio of the resistors R01 and R02, the power supply voltage which does not exceed the break-down voltage of the devices in the inner circuit can be supplied to the inner circuit. However, this operation is attained when the following equation (3) is satisfied among the voltage difference V12, the output voltage VOUT, and the voltage Vgs1 between the gate and the source of the PMOS transistor MOI.
V12 greater than VOUT+Vgs1xe2x80x83xe2x80x83(equation 3)
When the input voltage VIN, which does not satisfy the equation (3) is inputted, the output voltage is as shown by the following equation (4) and is dependent on the input voltage.
VOUT=V12xe2x88x92Vgs1xe2x80x83xe2x80x83(equation 4)
Accordingly, when a sufficiently large input voltage VIN is not supplied, the ratio of the voltage Vgs1 between the gate and the source to the voltage difference V12 is increased, so that a sufficiently large output voltage VOUT cannot be obtained. The MOS transistor M01 is necessarily required to have a higher breakdown voltage since a relatively larger voltage is applied in accordance with the input voltage VIN, and the threshold voltage Vgs1 of the MOS transistor M01 is higher than that of MOSFETs in the inner circuit since a relatively larger current supplied to the inner circuit flows through the MOS transistor M01. For example, the threshold voltage of the MOS transistors in the inner circuit can be reduced to about 0.6 volts by the miniaturization of the devices, while the threshold voltage of the MOS transistor M01 is required to be about 1.5 volts.
As described above, when the voltage loss of the voltage control circuit is increased, a minimum input voltage for normally operating the inner circuit is increased, so that, for example, in the contactless IC card, the deterioration of characteristics thereof such as reduction of communication distance occurs. It is necessary to reduce the voltage loss in the power supply circuit to be as small as possible in order to prevent such a characteristic deterioration. However, in a conventional series regulator in which means for stabilizing the power supply voltage are connected to an output side of the means for rectifying and smoothing a received electromagnetic wave, since a voltage, loss in the means for stabilizing the power supply voltage is large in the state in which electric power supplied to the IC card is small, it is necessary to increase the input voltage VIN for obtaining the lower limit operation voltage required for operation of the inner circuit, so that the communication distance is not extended.
It is an object of the present invention to provide a semiconductor integrated circuit device and a contactless electronic device having the power supply circuit realizing the production of a smoothed voltage stabilized with high efficiency and stable operation of the inner circuit. It is another object of the present invention to provide a contactless electronic device capable of lengthening communication distance. The above and other objects and novel features of the present invention will be apparent from the following description of the invention and the accompanying drawings.
According to a first aspect of the present invention, an AC voltage is applied to first and second input terminals, and a rectified current is supplied between the first and second input terminals by means of a rectifying transistor having a drain (or collector) connected to the second input terminal and a gate (or base) and a drain (or collector) connected through resistor means. A control voltage is produced by first voltage detection means so that a rectified voltage produced on the side of the source (or emitter) of the first rectifying transistor is equal to a predetermined reference voltage. A first voltage controlled current source produces a current in accordance with the control voltage and supplies the current to the first resistor means.
According to another aspect of the present invention, in a contactless electronic device including a power supply circuit for producing an internal voltage from electric power received by an antenna for receiving signals and electric power, in an inner circuit which operates by the internal voltage, and in a communication circuit which operates by the internal voltage and receives and transmits signals through the antenna, the power supply circuit supplies an AC voltage produced by the antenna to first and second input terminals, and it supplies a rectified current between the first and second input terminals by means of a rectifying transistor having a drain (or collector) connected to the second input terminal and a gate (or base) and a drain (or collector) connected through resistor means. A control voltage is produced by first voltage detection means so that a rectified voltage produced on the side of the source (or emitter) of the first rectifying transistor is equal to a predetermined reference voltage. A first voltage controlled current source produces a current in accordance with the control voltage and supplies the current to the first resistor means.